Radio-frequency transmission line



June 19, 1951 w. N. CHRISTIANSVEN RADIp-F'REQUENCY TRANSMISSION LINEFiled March 27, 1947 INCREASE 6 BY uw m ATTORN EY Patented June 19, 1951UNITED STATES toria,

Australia, assignor to Amalgamated Wireless (Australia) Limited, Sydney,New South Wales, Australia, a company of New South Wales ApplicationMarch 27, 1947, Serial No. 737,619 In Australia June 19, 1946 6 Claims.

The present invention relates to radio frequency transmission lines andmore particularly to means for matching the characteristic impedance ofa pair of multiple-Wire lines to the characteristic impedance of asingle multiple-wire line over a wide range of impedance values.

When open wire lines are employed for the transfer of high frequencyenergy from a transmitter to a remotely locamd antenna or from areceiving antenna to a remotely located receiver, it is desirablerespectively to prevent radiation from and pick-up by the transmissionline system.

In order to fulfill these requirements it has been the practice in thepast to employ multiplewire transmission lines. This type of linecomprises a plurality of conductors connected electrically in parallelfor conveyingcurrent in one direction, and another pluralit ofconductors for returning the current connected electrically in parallel,and so located that the loci of the electrical centres of both sets ofconductors coincide. Since alternating currents are being dealt with,the directions referred to are instantaneous only. With such anarrangement there is no physical displacement between the oppositeelectrical charges and there is therefore neither radiation orcollection of energy.

In transmission lines of this type, there are usually employed fourparallel conductors arranged as at the corners of an imaginary square,and at each end of the line diagonally opposite conductors are connectedtogether.

In certain applications involvin the use of multiple lines of the 4-wiretype it is necessary to effect a satisfactory impedance matchingconnection between a single -wire line and a pair of similar linesconnected in parallel. In the past when this requirement has arisen, andmatching at a plurality of frequencies is involved, the desiredconnection has been achieved by the use of a broad band impedancematching transformer.

This prior art method of coupling a single 4- wire line to a pair of4-wire lines, has not been entirely satisfactory because of resistancelosses introduced into the system by this form of coupling and itsliability to damage by lightning.

The principal object of the present invention is to overcome theabove-mentioned disadvantages and provide a transmission linearrangement for matchin the characteristic impedance of a pair offour-wire lines without employing the conventional transformer.

A further object of the invention is to provide a transmission linearrangement whereby a pair of 4-w1're lines may be conductivelyconnected to a single -wire line in impedance matching relationship.

The above objects are achieved in accordance with the present inventionpreferably by the use of a multiple-wire transmission line sectioninterposed between the ends of the pair of multiplewire lines and theends of the single multiple- Wire line, said transmission line sectioncomprising a plurality of conductors equal in number to the total numberof conductors in said pair of multiple-wire lines and arranged about acommon axis at equal radial distances therefrom. The foregoingarrangement is such that the conductors of said line section aredisposed about the circumference of an imaginary circle having adiameter at one end of said transmission line section equal to thediagonal dimensions of each of said pair of multiple-wire lines, theindividual conductors of which latter are alternately and sequentiallyconnected to separate and alternate conductors of said transmission linesection at said one end. The diameter of said imaginary circle at theother end of said transmission line section is equal to the diagonaldimensions of said single multiple-wire line whose individual conductorsare separately and sequentially connected to pairs of adjacentconductors of said transmission line section, the alternate conductorsof said line section being simultaneously and progressively varied inthe same direction of angular movement about the common axis of the saidtransmission line section to cause a variation in the spacing betweenadjacent conductors at opposite ends thereof.

For a more complete understanding of the invention and the manner inwhich it is to be carried out attention is now directed to the followingdescription in connection with the accompanying drawing in which:

Fig. 1 is a diagram illustrating the placement of the conductors of atransmission line according to the invention; and

Fig. 2 is an illustration of a practical construction of a transmissionline according to the invention.

In the exemplary arrangement covered by the following description, theinvention provides a matching system for connecting a pair of l-wirebalanced transmission lines to one 4-wire balanced transmission line. Inits simplest form the invention involves running the two sets of 4-wirefeeders along a common axis thus forming an 8- wire line. The impedanceof this 8-Wire line may be readily varied by rotating one set of 4-wireswith respect to the other set.

At the point in the system where the conductors of the two 4-Wire linescoalesce the conductors 2, 4, 6, 8 of one line and the conductors 3, 5,I, 9 of the other line, are alternately arranged and symmetricallydisposed in any convenient manner about at common axis to form an 8-wireline of octagonal cross section as shown in Fig. 1 of the drawing.Although in order to clarify the explanation of the invention, theconductors comprising the separate 4'-'wire lines" have been shown inthe drawing of different cross section, it is to be understood that all:of the conductors are preferably of the sameproportion and that thephysical dimensions of' both of: the 4-wire lines are the same. In thesecircumstances when the conductors of the two lines are brought togetherto form the 8-wire lineof1octagon'al cross section as described abovethey are located at each of the vertices of the octagonand are thussymmetrically disposed about the circumference. of .a..circle havingdiameter-equal xtO; the diagonal dimensions of each of the i-wireilinesandwhoseaxis coincides with the..a-x-is.-.of the compositeline.

Two conductors in each -wire line are shaded in the. drawing for thepurposes or identification.

.By rotating one set-of conductors 2-, 4;: 6;: 8. with respect of .theother set 3; 5, l, Sso that the angle formed by the. intersection or two.lines joining the-diametrically-: opposite conductors ofeach .4ewireline is caused to vary,.theWaveimpedance along the composite line can hecaused-to change inany desiredmanner, erg. exponentially-over arange-ofiimpedances greater than'two to one.

-It-has been found that there resultsa very" simple expression for thecharacteristic impedance of such a line, this bein where 'D is the'cliameterof' the circle containing all the wires,

d is'the diameter of the wire, is the angle of rotation shown in-thedrawing.

Alf. at the .end of the 8-wire line to which the pair of 4awire-linesare connected the conductors are disposedin the-physical arrangementshown .in.the.accompanying drawingthe angle 0 will be. .45. degrees and.the characteristicimpedance Z0 atthis end of the- 8ewire line will beequal to.half ..the value .ofthe .characteristic impedance of -each ofthe 4-wire lines. This facilitates an'impedancematching coupling betweenthe pair of 4- wirelines and the composite '8-wire line bydirectconnections.

.The characteristic impedance at theother end of the 8-wire line willdepend'u-pon thephysical relationshiprofthe conductors and the value ofthe angle 0 at that end.

By simply rotating one: setof 4-wires--.with respectto theother set theangle Biscaused to vary and it'ispossible'toadjust the characteristicimpedance of the line at that enduto any. 'Dredetermined value overrange.

a wide impedance tors' 2, 4, 6, 8 in a clockwise directionabout h axisof the line so as to decrease the value of the angle 0 thecharacteristic impedance of the 8- wire line may be increased to a valuesuch as will permit direct connection to a single l-wire .line inimpedance matching relationship. It is possible; also, .to vary theangle 9 and the ratio currentrequirdto pass along the line and-(iii)-:the maximum deviation from the correct transform'ationratio thatcan be tolerated. The

higherithetransformation ratio or the lower the maximum frequency or thesmaller the allowable ideviation, the longer must be the exponentialline.

'The number of supports required for such an exponential line will bedetermined often by the requirement of mechanical stability. fApartfromthis, @however, there is; a minimum'mnnber of 'supports'that can be usedif the exponentialform of the line is to be preserved. It is foundpossible at'the ends and one other pout.

:tl'fllflSfOIll'lfltlOllfflOlTl 131: ohms to 262 ohms.

one-design for such a line, illustrated in Fig. 2

with'the 8'-wire line, described here, to achieve a line that'inatwo-toone range of impedance departs by less than one-per cent from thetrue exponential form, when the line is supported only As an example ofthis consider a line designed for animpedance In "of the drawing;supports are provided atthe ends 1 pass through apertures and Over onehalf of the line the and 23 are provided with apertures 8| 32 and 33,respectively. 'Apertui'es 32 and 33 are of thesame diameter and smallerthan aperture 3|. Crossshaped members 4|, 42 and 43 'having feed:through insulators'2? located near the ends are arranged on one siderespectively of supports 2|,

'22 and23 and members 5|, 52 and 53 similarly fashioned are arranged onthe other side respectively, the rotatable complementary members 1 beingheld in place after adjustment by clamp action brought about by bolts 54of like fasteners. Insulators 21 are placedso that conductors Thedimensions of the line at the three supporting points are respectively:

(1) 0=6'7.5,D/d=1 90 (2) 0=22, D/d= (3) 0=6.2, -D/d=660.

' What I claim is:

1. Improvements in radio frequency transmission lines of themultiple-wire type, residing in an arrangement for varying .thecharacteristic impedance of a parallel connected pair of such lines overa Wide range of impedance values, said arrangement consisting indisposing the individual conductors of said lines in parallelrelationship with each other, and alternately and symmetrically about acommon axis, at equal distances therefrom, the arrangement being such asto provide for simultaneous rotation of the conductors of either of saidlines about said com- 'mon axis 'soas to vary the spacing betweenadjacent conductors.

2. Improvements in radio frequency transmission lines of themultiple-wire type, residing in an arrangement for Varying thecharacteristic impedance of a pair of parallel connected e-wiretransmission lines over a wide range of impedance values, saidarrangement consisting in disposing the individual conductors of said4-wire lines in parallel relationship with each other, and alternatelyand symmetrically about a common axis, at equal distances therefrom, thearrangement being such as to provide for simultaneous rotation of theconductors of either of said lines about said common axis so as to varythe spacing between adjacent conductors.

3. Improvements in radio frequency transmission lines of themultiple-wire type, residing in an arrangement whereby a pair ofparallel connected. i-wire lines may be directly connected to a single4-wire transmission line in impedance matching relationship, saidarrangement consisting in disposing the individual conductors of saidi-wire lines in parallel relationship with each other, and alternatelyand symmetrically about a common axis, at equal distances therefrom, thearrangement being such as to provide for simultaneous rotation of theconductors of either of said lines about said common axis so as to varythe spacing between adjacent conductors.

4. Improvements in radio frequency transmission lines of the multiplewire type, characterized by a multi-Wire transmission line sectioninterposed between the ends of a pair of multiplewire lines and the endsof a single multiple-wire line the impedance of which is to be matchedwith said pair, said transmission line section comprising a plurality ofconductors equal in numher to the total number of conductors in saidpair, and arranged alternately and symmetrically about a commonlongitudinal axis, the arrangement being adapted for simultaneouslyrotating said alternate conductors about said common axis to vary thespacing between adjacent conductors.

5. Improvements in radio frequency transmission lines of themultiple-Wire type, residing in an arrangement for varying thecharacteristic impedance of a pair of parallel connected fourwiretransmission lines over a wide range of impedance values, saidarrangement consisting in disposing the individual conductors of saidfour-Wire lines in parallel relationship with each other, andalternately and symmetrically about a common axis, at equal distancestherefrom to constitute an eight-wire line, the arrangement being suchas to provide for simultaneous rotation of the conductors of either ofsaid lines about said common axis so as to vary the spacing betweenadjacent conductors permitting of impedance matching coupling betweensaid eightwire line and said pair of four-Wire lines by directconnection.

6. Improvements in radio frequency transmission lines of themultiple-wire type, residing in an arrangement for varying thecharacteristic impedance of a pair of parallel connected fourwiretransmission lines over a wide range of impedance values, saidarrangement consisting in disposing the individual conductors of saidfour-wire lines in parallel relationship with each other, andalternately and symmetrically about a common axis, at equal distancetherefrom, the arrangement being such as to provide for simultaneousrotation of the conductors of either of said lines about said commonaxis so as to vary the spacing between adjacent conductors, saidarrangement of said lines being supported only at the ends thereof andat one other point.

WILBUR NORMAN CHRISTIANSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,860,052 Peterson May 24, 19322,165,087 Alford July 4, 1939 2,404,797 Hansen July 30, 1946 FOREIGNPATENTS Number Country Date 515,121 Germany Jan. 3, 1931

